1. Field of the Invention
This nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 10-2003-0042225 filed in KOREA on Jun. 26, 2003, the entire contents of which are hereby incorporated by reference.
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube capable of enhancing a characteristic of a shadow mask by optimizing a structural strength of the shadow mask.
2. Description of the Conventional Art
A cathode ray tube is a device for converting an electric signal into an electron beam and emitting the electron beam to a phosphor screen to realize an image. The cathode ray tube is widely used in the conventional art since excellent display quality is achieved at an affordable price.
A cathode ray tube will be explained with reference to attached drawings. FIG. 1 is a schematic view showing an example of a cathode ray tube of the conventional art. As shown in FIG. 1, the cathode ray tube includes a panel 101 of a front glass; a funnel 102 of a rear glass engaged to the panel 101 for forming a vacuum space; a phosphor screen 113 deposited on an inner surface of the panel 101 and serving as a phosphor; an electron gun 106 for emitting an electron beam 105 which makes the phosphor screen 113 emit light; a deflection yoke 107 mounted at an outer circumference surface of the funnel 102 with a predetermined interval for deflecting the electron beam 105 to the phosphor screen 113; a shadow mask 108 installed at a constant interval from the phosphor screen 113; a mask frame 109 for fixing and supporting the mask 108; and an inner shield 110 extending from the panel 101 to the funnel 102 for shielding external terrestrial magnetism and thus preventing deterioration of color purity by the magnetism.
Also, as shown in FIG. 2, the shadow mask 108 includes a perforated portion 108b formed as a dome shape of a predetermined curvature and having a plurality of apertures 108a through which the electron beam 105 passes, and a skirt portion 108c extending from a periphery of the perforated portion 108b in the tube axis (Z-axis) direction for being fixed to the mask frame 109.
In the conventional cathode ray tube, the electron beam 105 emitted from the electron gun 106 is deflected by the deflection yoke 107, passes through the plurality of apertures 108a of the shadow mask 108, and lands on the phosphor screen 113 deposited on the inner surface of the panel 101. Accordingly, the deflected electron beam 105 makes the phosphor formed at the phosphor screen 113 emit light, thereby achieving an image.
According to a recent trend of the cathode ray tube, the cathode ray tube becomes large, and a curved type panel that an inner surface and an outer surface have a small radius of curvature as shown in FIG. 3 is changing to a flat type panel that an outer surface is substantially flat as shown in FIG. 4.
Accordingly, as the panel 101 becomes large and its outer surface becomes substantially flat, a wedge ratio (%), a ratio of a peripheral thickness Td to a central thickness Tc (Td/Tc) of the panel 101 becomes great. According to this, a difference of an optical transmittance between a center and a periphery of the panel 101 becomes great and thus brightness of a screen becomes uneven. Also, as the panel 101 becomes large and its outer surface becomes substantially flat, a size of the shadow mask 108 also becomes large. Therefore, a curvature of the shadow mask 108 having a dome shape with maintaining a certain interval from an inner surface of the panel 101 becomes flat and a structural strength of the shadow mask 108 is lowered, thereby degrading an impact resistance of the shadow mask 108.
Meanwhile, in order to improve the unevenness of brightness of the panel 101, a tinted glass which makes a glass of the panel 101 have an optical transmittance ratio of 45%˜75% is applied to the panel 101 without a processing such as a coating on the panel 101. However, in case of the panel 101 to which the tinted glass is applied, an optical transmittance becomes lower from a center towards a periphery of the panel 101, and thus a uniformity of brightness is lowered. Accordingly, in order to solve this problem, to reduce a weight of the panel 101, and to reduce a damage in a thermal processing due to a difference of the thickness of the panel 101, in case that a center thickness of the panel is 10 mm˜12.5 mm, a method for reducing the wedge ratio as approximately 170%˜210% is considered. That is, by reducing the wedge ratio, a peripheral thickness of the panel 101 is reduced thus to increase an optical transmittance of the periphery of the panel 101 and to improve the brightness uniformity characteristic at the center and periphery of the panel 101. However, when the wedge ratio of the panel 101 is reduced, the inner surface of the panel 101 becomes flatter and thereby a curvature of the shadow mask 108 having a dome shape with maintaining a certain interval from the inner surface of the panel 101 becomes flatter thus to degrade a structural strength of the shadow mask 108. According to this, the impact resistance of the shadow mask 108 is more degraded.
Also, even if a method for reducing a thickness of the shadow mask 108 to reduce a weight thereof and a material cost is considered, there is a limitation to reduce the thickness of the shadow mask 108, and therefore, it is not sufficient due to a degradation of the structural strength of the shadow mask 108.
Therefore, a shadow mask capable of preventing the impact resistance thereof from being degraded by optimizing the structural strength of the shadow mask is much required in case that the panel becomes flat and large, in case that the tinted glass is applied to the panel, and in case that the thickness of the shadow mask is reduced.